On the synthesis and crystal structure of BaC2

By the reaction of BaCO3 with graphite in an are melting furnace single cry stals of BaC2 could be synthesized. Structural investigations confirm the t etragonal structure (space group: I 4/mmm, Z = 2) given in the literature. In another approach polycrystalline BaC2 of high purity could be prepared b y the reaction of elemental barium and graphite at temperatures of about 10 00 K. Temperature dependent X-ray powder investigations on this sample conf irm the phase transition to a cubic phase (space group: F m (3) over bar m, Z = 4) at about 520 K (1st order phase transition). At low temperatures a new monoclinic form of BaC2 (space group: C 2/c, Z = 4) was found which is isotypic to the crystal structure of ThC2 at room temperature. This structu re was refined from neutron TOF diffraction data at 20 K. (C) 1999 Elsevier Science B.V. All rights reserved.